The BGS Lexicon of Named Rock Units — Result Details

Retford Member

Mudstone and siltstone, greenish grey, intercalated with subordinate reddish-brown mudstone; thin beds of varicoloured fine- to medium-grained sandstone, laminated and micaceous, are common throughout. Veins and nodules of gypsum are common locally. A thin calcareous conglomerate occurs locally at the base.

Definition of Lower Boundary:

Slightly unconformable, at an abrupt upward change from red-brown pebbly sandstones of the Sherwood Sandstone Group to the greenish grey mudstones at the base of the Retford Member. In north Nottinghamshire, the Retford Member is separated from the Sherwood Sandstone Group by a tongue of reddish brown mudstone and siltstone that thickens towards the northeast.

Definition of Upper Boundary:

Conformable, within a gradational, upward transition from greenish-grey mudstones and siltstones of the Retford Member to the predominantly brown mudstones, siltstones and fine-grained micaceous sandstones of the overlying undifferentiated Tarporley Siltstone Formation.

Thickness:

Maximum 21m in northeast Nottinghamshire, thinning to 6m south of Ollerton, pinches out at the northern outskirts of Nottingham.

Geographical Limits:

Mapped at outcrop in central and north Nottinghamshire, and proved in boreholes in the adjacent subcrop to the east.

Smith, E G and Warrington, G. 1971. The age and relationships of the Triassic rocks assigned to the lower part of the Keuper in north Nottinghamshire, north-west Lincolnshire and south Yorkshire. Proceedings of the Yorkshire Geological Society, Vol.38, 201-227.